docs: def get_truncation_language() -> ParserElement:
      """Build a parser for protein truncations."""
      l1 = truncation_tag + nest(amino_acid(AMINO_ACID) + ppc.integer(TRUNCATION_POSITION))
      l1.setParseAction(_handle_trunc)
      l2 = truncation_tag + nest(ppc.integer(TRUNCATION_POSITION))
      l2.setParseAction(_handle_trunc_legacy)
      return l1 | l2